Geometrical Aspects of Gigantic Magneto-Electric Effect and Quantum Pump

Abstract

We study the magneto-electric (ME) effect from the viewpoint of the Berry phase connection and quantum adiabatic charge transport. The linear response theory for the electronic polarization P_el can be interpreted in terms of the flux or the fictitious magnetic field related to the Berry phase in the generalized momentum space including external parameters. An applied magnetic field modifies the spin configuration, induces adiabatic deformation of the Bloch wavefunction, and results in the electronic polarization. This provides a new mechanism for the gigantic ME effect. For a cyclic change of the applied magnetic field, even a quantized charge transport is possible. We also argue how the so-called depolarization field affects this novel mechanism of ME effects, based on mean-field analyses.